adccommunitymod (AutomationDirect) asked a question.
Fuses versus supplemental protectors
Created Date: December 04,2009
Created By: doug6949
**** This post has been imported from our legacy forum. Information in this post may be outdated and links contained in the post may no longer work.****
I am assembling a system using a 3hp GS2 drive. The print specifies a triple fuse block on the drive input. I try to avoid fuses since circuit breakers are considerably more convenient. Is there a valid reason for using fuses instead of circuit breakers? TNX, Doug
Created Date: December 04,2009
Created by: Do-more PE
Manufacturers recommend fuses because circuit breakers are not fast enough to protect the drive in the event of a significant power event.
Created Date: December 05,2009
Created by: BAK96
Not sure about the GS drives but I have experience on more than one occasion that by using fuse's and if one pops this can cook the drive by single phasing. Toshiba drives especially.
Created Date: December 07,2009
Created by: doug6949
Thank you for the input.
I don't have the manual with me at present so this is from memory. GS3 drives above 3hp have phase loss detect and will fault if one leg opens. A blown fuse should not cause damage to the drive.
Still, my disgust for fuse blocks makes me favor a circuit breaker. The recommended fuse block kits don't even have safety shields.
Doug
Created Date: December 10,2009
Created by: carmusic
i would use breakers, anyway if the drive make the fuse blow, most of the times it is because the drive has broken (short igbt or rectifier on it) and the fuse only protects wiring and risk against fire in the drive so does the breaker. As long as you have branch circuit protection ahead the breaker you are ok.
Created Date: March 08,2010
Created by: genebond
Most drive manufacturers reccomend fuses because that's the way they got the UL approval :) Which is better for an application is subjective.
As far as cooking a drive by 1 fuse blowing, I 've never seen this issue. I can't imagine a design which would do this. Granted, something else could go wrong, but normally single-phasing a drive input is not a cause for failure, just a tripping fault... typically UnderVoltage.
Created Date: April 05,2010
Created by: doug6949
At the time of my OP I was under the mistaken impression that supplementary protectors were circuit breakers. Four months of reading NFPA-70, NFPA-79, UL-489, and UL-1077, made me realize my error.
Since MCCB's are costly it looks like I am back to fuses in the motor circuits.
There will be a sub-panel in this application which also requires branch protection. Am I correct in assuming DIN rail mounted (Buss-type glass) fuses also meet branch circuit protection requirements?
Created Date: April 06,2010
Created by: krak
If the supplementary protectors are not circuit breakers, What exactly are they considered to be?
Created Date: April 06,2010
Created by: Do-more PE
To simplify it greatly, supplementary protectors are for protection between branch circuits and the load. IE you have one branch circuit feeding many loads, you could use a supplementary protector to protect each load.
There are restrictions on the types of loads that they can protect however. As Doug6949 implied it is heavy reading.
Created Date: April 06,2010
Created by: doug6949
Reading through several forums I get the impression that -
1. Supplementary protectors are commonly and incorrectly used as branch circuit protection, and -
2. Recent changes and/or clarifications to NEC are directed at stopping this practice.
I 've been building equipment for more than ten years using only supplementary protectors. They are cheap, easy to use, and readily obtained from AD. I can see how even those with more experience would make the same mistake (or simply be tempted to cut costs).
The present project is big, expensive, and falls under IEC-954-1 level 3 for risk assessment. Hence the need to follow the rules.
Eaton makes UL-489 circuit breakers for DIN rail mounting. Sure wish AD carried them.
Doug
Created Date: April 06,2010
Created by: Do-more PE
While I don't have details that I can share on what products that we will be launching, I can say that we will be launching a large number of parts again this year. Keep your eye on the forum and our main page for details as new products are launched.